Study on Initial Kinetics of CdSe Nanocrystals by a Combination of in Situ X-ray Absorption Fine Structure and Microfluidic Reactor

The initial nucleation and growth processes of CdSe nanocrystals in a microfluidic reactor are studied by in situ extended X-ray absorption fine structure (EXAFS) in conjunction with UV-visible absorbance and photoluminescence spectra. On the basis of a surface reaction kinetics equation, the analytical expressions of the particle size and concentration are proposed. The surface reaction rate constant calibrated by UV-visible absorbance spectra at longer reaction time (>2.4 s) was used to estimate the particle size and concentration within the first 2.4 s of reaction. A burst of nucleation at 1-2 s with the smallest nucleus size of similar to 1.3 nm was observed after rapidly heating the reaction solution in the microfluidic reactor. This initial nucleation burst was associated with a rapid particle size increase within similar to 3 s, and after that the growth rate was slowed. It is demonstrated that the combination of in situ EXAFS with a microfluidic reactor provides a valuable way for studying the kinetics of nanocrystals synthesis in solution.